1. Field of Invention
This invention relates to a gun launched projectile design which imparts force to a subcaliber projectile, so as to induce a specific level of yaw.
2. Description of Related Art:
A variety of projectile design options exist in the art that provide a means for gun launching objects whose cross-sectional area or shape disallows the use of an integral obturator seal, e.g. an object whose effective diameter is less than the bore diameter of the launcher. Techniques vary depending on the intended application, different techniques are used for laboratory research and for weaponized ammunition. One laboratory launch method is known as the push- launch technique.
A typical prior art push-launch projectile comprises a subprojectile, multi-piece sabot petals, pusher plate, and and obturator. The subprojectile is the test item. Typical subprojectiles are rod penetrators or aero-ballistic flight bodies. The multi-piece sabot petals are composed of a multiplicity of petals which provide lateral support and alignment for subprojectile while in in-bore. Once the projectile exits the muzzle, the sabot petals separate. The usual goal during sabot petal discard is to impart minimal disturbance to the subprojectile that could alter its trajectory or induce yaw.
Yaw is defined as the angle between the long axis of the subprojectile and the line defined by the trajectory of the center of gravity of the subprojectile. Yaw is usually broken into two components, a vertical pitch and horizontal yaw which are measured in an earth -based laboratory coordinate system..The pusher plate supports the subprojectile and sabot during in-bore acceleration. The obturator serves as a seal for the propellant gases and transfers pressure to the pusher plate. The items are not fastened to the sabot or subprojectile and on muzzle exit, separate due to their higher aerodynamic drag.
Upon exit from the gun muzzle, stagnation conditions are reached on the leading surface of the sabot upon which are machined conical sections giving a scoop shaped surface. The scoop surface is designed in such a way that the resulting air pressure induces a moment which causes the petals to lift from the front, pivoting on the subprojectile at the aft end. During this time the sabot petals are in contact with the subprojectile and thus can apply a mechanical load at the aft end of the subprojectile. Aerodynamic loads can also be applied to the subprojectile during the sabot discard process. Supersonic flow around the subprojectile create shock waves which impinge on the subprojectile, which in turn can lead to subprojectile disturbance.
Prior art sabot petals have been designed to have identical geometric and aerodynamic configuration. Thus any load induced by a discarding sabot petal is counteracted by the opposing sabot petal. This provides the best chance of low flight disturbance, which is the clear goal of the prior art.